As an apparatus for cooling an engine mounted at a vehicle such as an automobile, for example, a water-cooling type engine cooling apparatus circulating cooling water which is cooled at a radiator to the engine is known. The cooling water is circulated by a water pump, for example. A flow rate of cooling water is controlled by a flow control valve disposed at a flow path through which the cooling water flows.
JP2008-286311A which is hereinafter referred to as Reference 1 discloses a flow control valve controlling a flow rate of cooling water which cools an engine. The flow control valve includes a valve body in a cylindrical form. An up-down movement of the valve body controls the flow rate of the cooling water flowing through plural ports provided at a housing. The cylindrical valve body is driven by a motor, for example.
According to a flow control valve including a cylindrical valve body, highly pressurized cooling water may be normally supplied to an outer peripheral surface of the valve body from a water pump during a transition of the flow control valve from a closed state to an open state. Therefore, the water pressure of the cooling water may be a large load upon movement of the valve body. An actuator that drives the valve body thus needs sufficient driving force or driving torque, for example, for moving the valve body against the load caused by the water pressure. As a result, a cost increase resulting from a construction of a mechanism for driving the valve body, i.e., an increase in size of the actuator, for example, may be inevitable.
In order to overcome the above, according to a flow control valve disclosed in JP2006-29113A which is hereinafter referred to as Reference 2, a pressure regulation passage is provided so as to regulate pressures at axially opposed sides of a cylindrical valve body to be equal to each other. As a result, a driving load of an actuator is minimized in a case where the cylindrical valve body moves in an axial direction to thereby achieve a decrease in size of the actuator.
The flow control valve disclosed in Reference 2 includes two cylindrical valve bodies within a housing, specifically, a valve body for a radiator flow control and a valve body for a bypass flow control. The two valve bodies are constructed so that moving directions thereof are orthogonal to each other. Thus, the pressure regulation passage is arranged along each of the moving directions of the valve bodies, which may lead to a complicated construction. In addition, because the two valve bodies including the moving directions orthogonal to each other are provided within the housing, a portion of the flow control valve other than the portion where the actuator is provided increases in size. Further, according to the flow control valve disclosed in Reference 2, an outer peripheral surface of the cylindrical valve body is configured to slidably move relative to an inner surface of the housing. Thus, a seal member provided between the outer peripheral surface of the cylindrical valve body and the inner surface of the housing may be abraded, which may lead to water leakage therefrom.
A need thus exists for a flow control valve which is not susceptible to the drawback mentioned above.